Read head having conductive filler in insulated hole through substrate

ABSTRACT

A novel read head includes a substrate having a trailing face and a leading face opposite the trailing face. The substrate includes a first hole therethrough that extends continuously from the trailing face to the leading face. The read head also includes a read transducer disposed on the trailing face, and a first plurality of electrically conductive trailing connection pads disposed on the trailing face. A first insulative layer is disposed on an inner surface of the first hole. A first electrically conductive filler is disposed in the first hole but is insulated from the substrate by the first insulative layer. A first electrically conductive leading connection pad is disposed on the leading face and is electrically connected to the first conductive filler.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the field of informationstorage devices, and more particularly to head gimbal assemblies used ininformation storage devices.

2. Background of the Art

Information storage devices are used to retrieve and/or store data incomputers and other consumer electronics devices. A magnetic hard diskdrive is an example of an information storage device that includes oneor more heads that can both read and write, but other informationstorage devices also include heads—sometimes including heads that cannotwrite. For convenience, all heads that can read are referred to as “readheads” herein, regardless of other devices and functions the read headmay also perform (e.g. writing, micro-actuation, flying height control,touch down detection, lapping control, etc).

In a modern magnetic hard disk drive device, each read head is asub-component of a head gimbal assembly (HGA). The read head typicallyincludes a slider and a read/write transducer. The read/write transducertypically comprises a magneto-resistive read element (e.g. so-calledgiant magneto-resistive read element, or a tunneling magneto-resistiveread element) and an inductive write structure comprising a flat coildeposited by photolithography and a yoke structure having pole tips thatface a disk media. The typical read/write element requires fourelectrical connection terminals (i.e. so called “bond pads”) on the readhead. These four do not including any additional bond pads that may berequired for the manufacture and/or testing of the read head, such asbond pads for an electrical lapping guide (ELG) on the read head tocontrol lapping of the pole tips during manufacture.

The HGA typically also includes a suspension assembly with a laminatedflexure to carry the electrical signals to and from the bond pads of theread head. The HGA, in turn, is a sub-component of a head stack assembly(HSA) that typically includes a plurality of HGAs, an actuator, and aflex cable. The plurality of HGAs is attached to various arms of theactuator, and each of the laminated flexures of the HGAs has a flexuretail that is electrically connected to the HSA's flex cable. Modernlaminated flexures typically include electrically conductive coppertraces that are isolated from a stainless steel support layer by apolyimide dielectric layer. So that the signals from/to the head canreach the flex cable on the actuator body, each HGA flexure includes aflexure tail that extends away from the head along the actuator arm andultimately attaches to the flex cable adjacent the actuator body. Thatis, the flexure includes electrically conductive traces that extend fromadjacent the head and terminate at electrical connection points at theflexure tail. At the other end, the electrically conductive traces areelectrically connected to a plurality of electrically conductive bondingpads on the head.

The industry trend towards increasing areal data density hasnecessitated, for certain disk drive products, that additional featuresbe added to the read head. Each such additional feature requireselectrical connection to additional bonding pads per read head. Forexample, a microactuator for fine tracking control may be added to theread head to increase servo bandwidth and thereby facilitate an increasein the data track density of the disk drive (typically measured intracks per inch). A heater for flying height actuation may also be addedto the read head to allow the separation between the read head and thedisk media to be greater when not reading or writing (and therebyimproving tribological performance of the read head), while causingthermal expansion that temporarily brings the read/write transducercloser to the disk media while reading and writing (and thereby obtainacceptable signal amplitude). Also, a touch-down sensor may be added tosense when the read head contacts the disk surface during operation.

However, in most applications, the head cannot be made larger toaccommodate the additional bonding pads associated with suchimprovements. On the contrary, as a general trend, heads have becomesmaller for various important reasons (e.g. cost, dynamic response tomechanical shock, etc), and such trend is unlikely to reverse. Althoughsome number of additional bonding pads might be accommodated by makingthe bonding pads smaller, the size of bonding pads in contemporaryread/write heads has already been reduced to the point where electricalinterconnect during manufacture has become challenging and difficult.Accordingly, there is a need in the art for HGA designs that canfacilitate the practical electrical connection of conductive traces ofthe flexure to more bonding pads on the head.

SUMMARY

A novel read head is disclosed. The read head includes a substratehaving a trailing face and a leading face opposite the trailing face.The substrate includes a first hole therethrough that extendscontinuously from the trailing face to the leading face. The read headalso includes a read transducer disposed on the trailing face, and afirst plurality of electrically conductive trailing connection padsdisposed on the trailing face. A first insulative layer is disposed onan inner surface of the first hole. A first electrically conductivefiller is disposed in the first hole but is insulated from the substrateby the first insulative layer. A first electrically conductive leadingconnection pad is disposed on the leading face and is electricallyconnected to the first conductive filler.

A novel method for fabricating a read head is also disclosed. The methodincludes depositing conductive filler into a plurality of holes thatextend through a wafer, and fabricating a read transducer on the wafertop surface. Each of the holes extends from a wafer top surface to awafer bottom surface. Each of the holes includes an inner surface thatincludes an insulative layer. The method also includes depositing aplurality of electrically conductive leading connection pads on thewafer bottom surface. The plurality of electrically conductive leadingconnection pads are in electrical contact with the conductive filler.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is top perspective view of a disk drive capable of including anembodiment of the present invention.

FIG. 2 is an exploded perspective view of the distal end of a headgimbal assembly (HGA) according to an embodiment of the presentinvention.

FIG. 3A is a back perspective view of read head, according to anembodiment of the present invention.

FIG. 3B is a front perspective view of the read head of FIG. 3A.

FIG. 4A is a top view of a wafer shown during the manufacture of readheads according to an embodiment of the present invention.

FIG. 4B is a side cross-sectional view of the wafer of FIG. 4A.

FIG. 5A is a top view of a wafer shown during the manufacture of readheads according to an embodiment of the present invention.

FIG. 5B is a side cross-sectional view of the wafer of FIG. 5A.

FIG. 6A is a top view of a wafer according to an embodiment of thepresent invention, after the conventional fabrication of read/writetransducers.

FIG. 6B is a side cross-sectional view of the wafer of FIG. 6A.

FIG. 7A is a top view of a wafer shown during the manufacture of readheads according to an embodiment of the present invention.

FIG. 7B is a side cross-sectional view of the wafer of FIG. 7A.

FIG. 8 is a side perspective view of an HGA according to an embodimentof the present invention, shown during HGA assembly.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1 is top perspective view of a disk drive 100 capable of includingan embodiment of the present invention. The disk drive 100 includes adisk drive base 102 and two annular magnetic disks 104. The disk drive100 further includes a spindle 106, rotably mounted on the disk drivebase 102, for rotating the disks 104. The rotation of the disks 104establishes air flow through recirculation filter 108. In otherembodiments, disk drive 100 may have only a single disk, oralternatively, more than two disks.

The disk drive 100 further includes an actuator 110 that is rotablymounted on disk drive base 102. Voice coil motor 112 rotates theactuator 110 through a limited angular range so that at least one headgimbal assembly (HGA) is desirably positioned relative to one or moretracks of information on a corresponding one of the disks 104. Theembodiment of FIG. 1 includes four HGAs 114, each of which correspondsto a surface of one of the two disks 104. However in other embodimentsfewer or more HGAs may be included depending on the number of disks 104that are included and whether the disk drive 100 is depopulated. EachHGA 114 includes a read head (not depicted in FIG. 1) for reading andwriting data from and to one of the disks 104. The actuator 110 mayoccasionally be latched at an extreme angular position within thelimited angular range, by latch 120. Electrical signals to/from the HGAs114 are carried to other drive electronics via a flex cable 122 and flexcable bracket 124.

FIG. 2 is an exploded perspective view of the distal end of an HGA 200according to an embodiment of the present invention. Now referringadditionally to FIG. 2, the HGA 200 includes load beam 202 and a readhead 210. The read head 210 includes a slider substrate 212 having atrailing face 208 and a leading face 216 opposite the trailing face 208.The slider substrate 212 preferably comprises AlTiC or silicon. Theslider substrate 212 also includes an air bearing surface 214 that issubstantially orthogonal to the trailing face 208, and that includes aread/write transducer (too small to be practically shown in the view ofFIG. 2, but disposed on the trailing face 208). In certain embodiments,the read/write transducer is preferably an inductive magnetic writetransducer merged with a magneto-resistive read transducer. The purposeof the load beam 202 is to provide vertical compliance for the read head210 to follow vertical undulations of the surface of a disk (e.g. disk104 of FIG. 1) as it rotates, and to preload the air bearing surface ofthe read head 210 against the disk surface by a preload force that iscommonly referred to as the “gram load.”

The HGA 200 also includes a laminated flexure 204 attached to the loadbeam 202. The head 210 is attached to a tongue 206 of the laminatedflexure 204. A first purpose of the laminated flexure 204 is to providecompliance for the head 210 to follow pitch and roll angular undulationsof the surface of the (e.g. disk 104) as it rotates, while restrictingrelative motion between the read head 210 and the load beam 202 in thelateral direction and about a yaw axis. A second purpose of thelaminated flexure 204 is to provide a plurality of electrical paths tofacilitate signal transmission to/from the read head 210.

For that second purpose, the laminated flexure 204 includes a pluralityof electrically conductive traces 218 that are defined in anelectrically conductive layer 220, and that are isolated from a supportlayer 222 by a dielectric layer 224 that is disposed between the supportlayer 222 and the electrically conductive layer 220. The plurality ofelectrically conductive traces 218 of the flexure 204 are electricallyconnected to a first plurality of electrically conductive trailingconnection pads 230 on the trailing face 208 of the read head 210, by aplurality of 90° bonds 228.

In the embodiment of FIG. 2, the first plurality of electricallyconductive trailing connection pads 230 preferably comprises copper orgold. The plurality of 90° bonds 228 preferably comprises solder orgold. The conductive traces 218 may comprise copper, the support layer222 may comprise stainless steel and/or another suitable structuralmaterial, and the dielectric layer 224 may comprise polyimide, forexample. In certain embodiments, the electrically conductive layer 220comprises a copper layer having a thickness that is at least 5 micronsbut no more than 15 microns. In various regions of the laminated flexure204, one or more of the layers may be absent (e.g. removed by etching).

FIG. 3A is a back perspective view of the read head 210, according to anembodiment of the present invention. FIG. 3B is a front perspective viewof the read head 210. Now referring additionally to FIGS. 3A and 3B, theread head 210 includes a first plurality of electrically conductivetrailing connection pads 230 on its trailing face 208. The slidersubstrate 212 includes a plurality of holes 250 therethrough, eachextending continuously from the trailing face 208 to the leading face216. In the embodiment of FIGS. 3A and 3B, each of the plurality ofholes 250 defines a hole longitudinal axis that is normal to thetrailing face 208. Preferably, each of the plurality of holes 250defines a hole diameter in the range 10 μm to 100 μm. In the embodimentof FIGS. 3A and 3B, the length of each hole 250 is approximately equalto a distance between the leading face 216 and the trailing face 208,measured normal to the trailing face 208.

In the embodiment of FIGS. 3A and 3B, each of the plurality of holes 250contains an electrically conductive filler 252 that is insulated fromthe slider substrate 212 by an insulative layer. The insulative layer istoo thin to be clearly shown in FIGS. 3A and 3B, but it is disposed onthe inner surface of each hole (as will be shown and described laterherein). Preferably, the electrically conductive filler 252 comprises anelectrically conductive material having a low coefficient of thermalexpansion (e.g. tantalum), and/or an electrically conductive material(e.g. TiC) having a coefficient of thermal expansion that may be similarto that of the slider substrate 212.

As is shown in FIGS. 3A and 3B, the read head 210 also includes a firstplurality of electrically conductive leading connection pads 240disposed on the leading face 216 of the slider substrate 212, and eachof the first plurality of electrically conductive leading connectionpads 240 is connected to the electrically conductive filler 252 of arespective hole 250.

FIG. 4A is a top view of a wafer 400 shown during the manufacture ofread heads according to an embodiment of the present invention. FIG. 4Bis a side cross-sectional view of the wafer 400. The number and stepdensity of features shown on the wafer 400 has been reduced in FIGS. 4Aand 4B, so that the spacing between features may be artificially largeand/or the size of features may be artificially large, for clarity ofillustration. The water 400 includes a wafer top surface 402, and anopposing wafer bottom surface 404. A plurality of holes 450 is createdthrough the wafer 400, for example by laser drilling, ultrasonicdrilling and/or a plurality of pins in the wafer mold. A water jet mayalso be used to create the holes, alone or in conjunction with anotherform of drilling. Each hole 450 extends through the wafer 400 from thewafer top surface 402 to the wafer bottom surface 404. Preferably, eachof the plurality of holes 450 defines a hole diameter in the range 10 μmto 100 μm. The wafer 400 preferably comprises AlTiC because thatmaterial has desired properties as the slider substrate for read heads(that are ultimately diced apart from the wafer sometime after a mergedor read transducer is fabricated on the wafer top surface 402).

An insulative layer 454 is formed on an inner surface of each of theplurality of holes 450, for example by high temperature annealing of theAlTiC wafer substrate (e.g. preferably to create an insulative titaniumoxide layer having a thickness in the hole in the range 10 to 20angstroms), and/or by atomic layer deposition (ALD) of aluminum oxide(e.g. preferably to a thickness in the hole in the range 0.05 microns to0.1 microns). In certain alternative embodiments, if the wafer substratematerial is silicon, then a silicon oxide insulative layer may bethermally grown on the substrate (and in the hole) by conventionalmethods. The insulative layer may also comprise magnesium oxide and/orother insulative oxides or insulative materials. Note that, herein,if/when more than one insulative layer is disposed between a conductivestructure and the substrate, then each of the insulative layers is saidto be insulating that conductive structure from the substrate.

Electrically conductive filler 452 is deposited into the plurality ofholes 450 that extend through the wafer 400. In certain embodiments, theelectrically conductive filler 452 preferably comprises an electricallyconductive material such as TiC that has a coefficient of thermalexpansion (CTE) that approximately matches the CTE of the wafersubstrate material. In certain other embodiments, the electricallyconductive filler 452 may preferably comprise a conductive metal thathas a relatively low CTE such as tantalum. Alternatively, otherconductive metals (e.g. gold or copper) may be used. In certainembodiments, after filling the holes 450 with the conductive filler 452,the wafer may be fired to bind or adhere the conductive filler 452 tothe inside of the insulated holes 450 and/or to bind grains or particlesof the conductive filler 452 to each other to form bound conductivestuds through the insulated holes 450.

FIG. 5A is a top view of a wafer shown during the manufacture of readheads according to an embodiment of the present invention. FIG. 5B is aside cross-sectional view of the wafer of FIG. 5A. As with the precedingfigures, the number and step density of features shown on the wafer 500has been reduced in FIGS. 5A and 5B, so that the spacing betweenfeatures may be artificially large and/or the size of features may beartificially large, for clarity of illustration.

The wafer 500 of FIGS. 5A and 5B is in a more advanced stage ofmanufacture than the wafer 400 of FIGS. 4A and 4B, because it is shownafter the wafer 400 has been lapped by conventional lapping methods topolish and planarize the wafer top surface 402 (and, optionally, thewafer bottom surface 404 also).

After lapping, the wafer top surface 402 is subjected to the variousconventional deposition, masking, and etching steps required tofabricate read/write transducers. For example, FIGS. 6A and 6B depict awafer 600 according to an embodiment of the present invention, after theconventional fabrication of read/write transducers 670. As inconventional read heads, each of the read/write transducers 670 may beelectrically connected to a plurality of electrically conductivetrailing connection pads 630. However, unlike in conventional readheads, the top surface 402 of wafer 600 may accommodate additionaldevices for each read head (e.g. a microactuator, heater for dynamicflying height control, touch-down sensor, and/or electric lapping guide,etc) because such additional devices (and/or conductors of the readwrite transducer 670 itself) may be electrically connected to theconductive studs 652 through the insulated holes 650 rather than only tothe plurality of electrically conductive trailing connection pads 630.

Note that in the embodiment of FIG. 6B, the plurality of electricallyconductive trailing connection pads 630 are insulated from the wafer topsurface 402 (which becomes the trailing face of each read head) by atrailing face insulative layer 634. However, trailing face insulativelayer 634 may be patterned by conventional methods when deposited, toallow electrical connections to be made to the read write transducer670, and the conductive studs 652, as desired.

Next, back-grinding of the wafer bottom surface 404 may be optionallyaccomplished to significantly reduce the wafer thickness, if it isdesired to shorten the length of the manufactured read heads to be lessthan the starting wafer thickness. For example, back-grinding of thewafer bottom surface 404 may reduce an overall thickness of the wafer600 by at least 300 μm. Hence, in certain embodiments of the presentinvention, the length of each of the plurality of holes 650 when created(e.g. drilled) and when insulated, may be significantly greater than thelength of each of the plurality of electrically conductive studs 652 andinsulated holes 650 through the length of each finally manufactured readhead. In this regard, each of the plurality of insulated holes 650preferably defines a hole length in the range 500 μm to 1300 μm,depending on the preferred thickness of the wafer during fabrication ofthe read/write transducers 670, and depending on the preferred length ofthe finished read heads. In certain embodiments, the hole length ispreferably approximately 1235 μm. In certain other embodiments, the holelength (e.g. after optional back-grinding) preferably may beapproximately 850 μm. After optional backgrinding, the wafer bottomsurface 404 may be polished.

FIG. 7A is a top view of a wafer shown during the manufacture of readheads according to an embodiment of the present invention. FIG. 7B is aside cross-sectional view of the wafer of FIG. 7A. As with the precedingfigures, the number and step density of features shown on the wafer 700has been reduced in FIGS. 7A and 7B, so that the spacing betweenfeatures may be artificially large and/or the size of features may beartificially large, for clarity of illustration.

The wafer 700 of FIGS. 7A and 7B is depicted in a more advanced stage ofmanufacture than the wafer 600 of FIGS. 6A and 6B, because it is shownwith a plurality of electrically conductive leading connection pads 780disposed on the wafer bottom surface 404 (which becomes the leadingfaces of the read heads). In the embodiment of FIG. 7B, it can be seenthat each of the plurality of electrically conductive leading connectionpads 780 is electrically connected to a respective one of the pluralityof electrically conductive studs 652 (which correspond to theelectrically conductive filler filling each of the plurality ofinsulated holes 650). Also in the embodiment of FIG. 7B, each of theelectrically conductive leading connection pads 780 is insulated fromthe wafer bottom surface 404 (which becomes the leading faces of theread heads) by a leading face insulative layer 784. This may serve toprevent shorting between the electrically conductive leading connectionpads 780 through the wafer substrate. Preferably, the leading faceinsulative layer 784 is deposited on the wafer bottom surface 404 as abottom surface insulative layer that is patterned so that the conductivefiller/studs 652 are exposed, before depositing the plurality ofelectrically conductive leading connection pads 780. For example,regions of the leading face insulative layer 784 that overlie theconductive filler/studs 652 may be opened using wet etch or ion milling.Preferably but not necessarily, each of the electrically conductiveleading connection pads 780 may be fabricated by first depositing apatterned seed layer (e.g. copper underlayer) and then depositing apatterned pad material (e.g. gold coating) upon the seed layer.

FIG. 8 is a side perspective view of an HGA according to an embodimentof the present invention, shown during HGA assembly. FIG. 8 depicts theelectrical connection of a plurality of electrically conductive traces218 (that are defined in an electrically conductive layer 220 of alaminated flexure 204) to the plurality of electrically conductiveleading connection pads 780 and to the plurality of electricallyconductive trailing connection pads 630 of a head 710. The head 710 mayhave been among a plurality of read heads cut from the wafer 700, forexample.

The electrical connections 228 between the plurality of electricallyconductive trailing connection pads 630 and the plurality ofelectrically conductive traces 218, and the electrical connections 828between the plurality of electrically conductive leading connection pads780 and the plurality of electrically conductive traces 218, may be madeby solder jet bonding, ultrasonic gold ball bonding, ultrasonic wedgebonding, solder bump bonding, or reflow soldering, for example. FIG. 8depicts a bonding tip 822 creating the electrical connections 228between the plurality of electrically conductive trailing connectionpads 630 and the plurality of electrically conductive traces 218.

Bonding tip 824 creates the electrical connections 828 between theplurality of electrically conductive leading connection pads 780 and theplurality of electrically conductive traces 218. In the embodiment ofFIG. 8, the bonding tips 822 and 824 may be conventional bonding tipsfor solder jet bonding, for ultrasonic gold ball bonding, for ultrasonicwedge bonding, or for another conventional method to create 90°electrical connections.

In the foregoing specification, the invention is described withreference to specific exemplary embodiments, but those skilled in theart will recognize that the invention is not limited to those. It iscontemplated that various features and aspects of the invention may beused individually or jointly and possibly in a different environment orapplication. The specification and drawings are, accordingly, to beregarded as illustrative and exemplary rather than restrictive.“Comprising,” “including,” and “having,” are intended to be open-endedterms.

1. A read head comprising: a substrate having a trailing face and aleading face opposite the trailing face, the substrate including a firsthole therethrough that extends continuously from the trailing face tothe leading face; a read transducer disposed on the trailing face; afirst plurality of electrically conductive trailing connection padsdisposed on the trailing face; a first insulative layer disposed on aninner surface of the first hole; a first electrically conductive fillerdisposed in the first hole but insulated from the substrate by the firstinsulative layer; a first electrically conductive leading connection paddisposed on the leading face and electrically connected to the firstconductive filler.
 2. The read head of claim 1 wherein the readtransducer and the first plurality of electrically conductive trailingconnection pads are insulated from the trailing face by a trailing faceinsulative layer.
 3. The read head of claim 1 wherein the firstelectrically conductive leading connection pad is insulated from theleading face by a leading face insulative layer.
 4. The read head ofclaim 1 wherein the first hole defines a hole longitudinal axis that isnormal to the trailing face.
 5. The read head of claim 1 wherein thefirst hole defines a hole diameter in the range 10 μm to 100 μm.
 6. Theread head of claim 1 wherein the first insulative layer defines a firstinsulative layer thickness in the range 0.05 μm to 0.1 μm.
 7. The readhead of claim 1 wherein the first insulative layer defines a firstinsulative layer thickness in the range 10 Å to 20 Å.
 8. The read headof claim 1 wherein the first insulative layer comprises Al₂O₃.
 9. Theread head of claim 1 wherein the substrate comprises AlTiC or silicon.10. The read head of claim 1 wherein the electrically conductive leadingconnection pad comprises copper or gold.
 11. The read head of claim 1further comprising a write transducer merged with the read transducer.12. The read head of claim 1 wherein the electrically conductive fillercomprises TiC.
 13. The read head of claim 1 wherein the first holedefines a hole length in the range 500 μm to 1300 μm.
 14. The read headof claim 13 wherein the hole length is equal to a distance between theleading face and the trailing face, measured normal to the trailingface.
 15. The read head of claim 14 wherein the hole length isapproximately 850 μm.
 16. The read head of claim 15 wherein the holelength is approximately 1235 μm.
 17. The read head of claim 1 whereinthe substrate further includes a second hole therethrough that extendscontinuously from the trailing face to the leading face, and wherein theread head further comprises a second insulative layer disposed on aninner surface of the second hole, and a second electrically conductivefiller disposed in the second hole but insulated from the substrate bythe second insulative layer, and a second electrically conductiveleading connection pad disposed on the leading face and electricallyconnected to the second conductive filler.
 18. The read head of claim 17wherein the substrate includes a plurality of holes therethrough thatextend continuously from the trailing face to the leading face, theplurality of holes including the first and second holes, and wherein theread head includes a plurality of electrically conductive leadingconnection pads disposed on the leading face, the plurality ofelectrically conductive leading connection pads including the first andsecond electrically conductive leading connection pads.